found a kitten in a box

She's pretty small, maybe seven or six weeks? I probably wouldn't have noticed her except her little head was peering out and I was driving slowly because I thought it was a garage sale sign. She was on a corner in a cardboard box (I had no clue people actually left kittens out like that! Especially in summer here where it's so hot!) I figured, I have a cat that is due any day and she could help take care of her. She's mostly black and felt really hot, panting and mewing.

When I walked in my cat hissed and growled, and the kitten did right back, even though she's a small fraction of the size of my cat! She's spunky.

My boy cat (he's getting neutered in a couple days, no worries) is locked up in the bathroom and didn't care at all about the kitten, just sniffed her a bit and was more interested in the milk I had and being petted.

Since I've already got so many vet bills with fixing my two cats (and the kittens before they go to their new homes) I can't afford to have her checked up for another couple weeks. She drank maybe an eighth of a teacup full of warm milk, but none of the water or kibble I offered.

In your experience, what's the best thing to feed a stay kitten (probably undernourished), and what can I do to help her get along with my girl cat? I don't want to send her to the humane society since they're so full already, when I am able to take her in. Is it too soon to give her flea medication? I haven't seen any on her but I don't want her giving them to my cats if she has them.

I thought she might enjoy having other kittens to play with when my cat gives birth. Is it likely my cat will even let her near the kittens when they're born?

I've added some pictures of her. She's climbed right into my lap and been asleep most of the time, and mews if I leave the bathroom, even though Pi is here with her and even bathed her face and ears. I don't know how long she was out there, but not more than two days, because the box want there last time I drove by that stop.

My guess she wasnt there very long. Less than a day.  Otherwise she would be more thirsty and or weak by sheer dehydration.  Its hot now, as you say..

Also, she isnt no stray in the words meaning.  She was dumped, so probably she had an owner.   How good caretaker this owner was, we dont know.  Bad enough to dump her...  At least he dumped her where she would be found. 

Some do dump them in a closed box in the middle of the woods.... Gods wrath on such villains

Tx for caring!

ps.  If you can get  goat milk, its better than cow milk.  KMR is a possibility too.  

The way momma and her are acting is very normal. Momma cat will either hate the new kitten or start following her around and licking on her etc. And it really depend on the cat, however hormones may overcome momma cats hatred of the new kitten and they may bond really well. Just give them some time.

I suggest blocking off a small quiet area for the new kitten with food and water and a litter box. That way you can see how her eating is progressing plus she will feel safe enough to actually eat and drink

As far as flea and worm mess go I suggest you either comb her or try giving her a bath because over the counter flea stuff is usually more harmful and it's not really good for kittens at all especially one so young.

As far as getting her nutrients up I would see if somewhere near you sells kitten milk. It comes either as a liquid or powder - I've heard that the powder is better but I've only ever used the liquid. You likely can get this from the pet section of any chain store or at a dollar store (or similar)
Wet food might also be tempting enough to et her eating and it will give her some fluids.

One last thing - cows milk is not good for kittens. It upsets their stomachs and can give them diarrhea (I've also heard that it will give them worms)

Good luck! You are a wonderful person to bring her in!!!

Thank you both very much for your quick response! I'll avoid the cow's milk then and see if I can find any kitten milk. Hopefully they'll all get along soon.