Help!! Vomiting, not eating/drinking, weight loss, and not using the bathroom

My poor cat Lily is very sick. She's an 11 year old indoor cat and has always been incredibly healthy before this. Lily started acting strange this past Wednesday. Usually she's very active and playful and loves attention. 4 days ago, Lily insisted on coming into my bedroom where I was and would not leave this one specific spot. In this spot she would look like she was comfortable for a few seconds and wanted to sleep, then quickly reposition herself repeatedly for hours. I thought this behavior was a bit odd so I told my family about it. She seemed like she was uncomfortable.
The next day her behavior was standoffish, and she kept to herself most of the day by hiding.
Friday, I noticed that it looked like she had not been eating or drinking very much of her food. The problem has persisted and took a turn for the worse Saturday morning. My main concern was that she was not drinking any water. She wasn't moving around much. So I decided I should physically bring water to her. When I did so, Lily drank quite a bit which seemed like a good sign. However within 30 minutes she vomited a milky white substance. She did this several times that night. This Sunday morning my family and I did the same thing bringing her water and she drank some and kept it down for awhile, so we tried brining her soft food that wouldn't be hard for her to chew, considering how weak she was acting. She got sick once again in the next hour from the food. There are also no signs she has used her litterbox.
We went in to the one vet that we found open on a Sunday. The whole time she was meowing and shaking, and is not very nice to strangers. She swatted at the vet one time (she doesn't have claws) and he immediately seemed to shut down and seemed unwilling to help. All he said was that sometimes cats have problems due to old age. He recommended they keep her overnight, get bloodwork, and do some barium exams with x-ray. The cost for everything he suggested would have been 2000 dollars upfront, and my family simply did not have the money. All of this seemed very extreme when the doctor would not even give any idea of possible threats...he just repeated saying how old she was (even though our other cat lived to be 19). The assistant who was helping then suggested we give her an antibiotic shot that would release over a 2 week time span after she heard we couldn't afford everything the vet wanted to do. This was the only thing we really could afford to do upfront, but we don't even know what we should be expecting. I know the blood work would should liver or kidney issues, and the X-ray would show any blockage or anything. The only thing I can think of she may have gotten ahold of was the string to my younger brothers birthday balloon. However when I voiced this concern the doctor said as an old cat it's unlikely she would do that. Every bit of information I provided was quickly dismissed. He didn't even bother inspecting her mouth or feeling for swelling in her stomach or anything of the sort. He was in the room for all of two minutes which was extremely frustrating when we're all so concerned.
We just want the best for our cat. I grew up with her. We're planning on checking out another vet who would allow us to make payments for tomorrow. In the meantime is there anything we can do? I've tried bringing her water and she won't even drink it now. And I know she won't be able to keep down any food, even though I know how much she needs it. If we need to force feed her or something wha should we feed her? I'm so scared for her and seeing her this way is just breaking my heart[emoji]128546[/emoji]

if she is not getting enough water she could be dehydrated-they should have done subfluids on her and a shot of cerenia for nausea.

is there another er in the next town over you can take her?

No where else remotely close to us is open until tomorrow unfortunately.
But I think there is some good news! We went to a pet store to try to find a syringe to feed her with and we picked up some soft food while there. The stuff we picked up was very watered down and before using the syringe we tried to see if she would eat on her own and she scarfed the little bit we gave her down! Not if she'll be able to keep it down, but still hopefully she'll be getting some nutrients. The people at the store were surprisingly much more helpful than our vet with their recommendations

Did you get her to another Vet, or did she start eating, drinking, and using the bathroom like normal?  If everything isn't back to normal, I would definitely get her seen by another Vet, as she is NOT too old to have played with and eaten a string.  11 is NOT really old in a cat.  It is considered a senior, but goodness, cats still play long after that.  Good grief ,  as you said, you had a cat who lived to be 19!

Hope everything is OK

She is eating again and she's holding it down for a lot longer than she was before, but she is still getting sick occasionally. I'm hoping that with the amount of water we're mixing in with the soft food she's getting enough nutrients to hold her over. She's definitely more responsive than before. She also did pee last night, but no bowel movements still. We're trying to get her to the vet again tomorrow. It's just hard when we don't have very much money to help her as much as we want to. Thank you for the reply!