University issues!! Cat separation anxiety?

Hi I am becoming concerned about my sisters cat. she's a gorgeous one year old British short hair cross, she is nuetered and has no medical conditions, she is called pixie. they have a really strong bond and my sister spent every minute of every day with her. Last month my sister went away to university and left pixie behind with the family and her house mate Dylan, a 9 month old Birman kitten, they usually get on really well. He is neutered and very very friendly ad cuddling. They sleep together and groom each other and have never had any serious issues or fights as they have lived togetehr since Dylan was 13 weeks old. She seemed to be acting fairly normally,I didn't notice any signs of stress or anything. However her and Dylan did seem to be having more squabbles than normal, never anything serious he is just quite a lot bigger than her and sometimes I think he plays a bit rough and she has to hiss to warn him off. However this has only happened a few times in the last month. Yesterday my sister came home from uni for a visit after 3 weeks away and pixie seemed to be ignoring her and acting upset and sulky and running away. She was only acting like this to my sister and was being her normal cuddly self with everyone else. The next day pixie was much better and was acting normal again with my sister but we came home from going out to dinner in the evening and she had urinated on the sofa, and urinated and defacated on the bed in the spare room. There was no diarreah and her urine was normal and Her litter box was clean and accessible. Could this be to do with her missing her owner or being confused about her abscence and return? Or is it more likely to be a territorial issue with Dylan? It just seemed a coincidence that this all happened the weekend her owner returned!

Anyone experienced anything similar? Or have any advice as we don't want this happening every time she comes home for a visit!! Plus we are worried pixie may be distressed and suffering without her owner :-(.

Thanks in advance!

I can relate to this experience.  Last year my son left for college.  His cat, Jake was so attached to him.  When he left Jake was so very sad.  We also have another cat and for awhile they just ignored each other.  I made sure that I gave Jake lots of extra attention.  He had to learn to find his way in the world without his best buddy ( my son).  It took time.  The first time my son came home for a visit, Jake ignored him and didn't even want him to hold him or pet him for the first day.  My son was so upset.  Yet after a day Jake was back to his old self.  Yet my son left after just a few days and Jake was so confused.  He started having stress pee issues.  He would run to the box and just pee a little tiny bit.  I took him to the vet and he did not have an infection, it was all just stress related.  He did not understand how his companion of 7 years was no longer around. 

A few things that helped:.  Lots of play time.  After each play time a reward of a special treat or snack. 

Feliway diffusers. These helped to calm him.  Also I used Composure liquid max which is a non sedating calming supplement that helps with stress.  You can also find it in treat formula, but some cats don't like the taste of the treats and it can take 3 or more 2x a day for it to work.  The liquid is just 1/2 t. in the morning wet food and 1/4 t. in the evening.  You can find both products for decent prices on Amazon.  They are a bit expensive, but they do help.

Each visit from my son was easier and easier as Jake adjusted.  Then my son came home for 3 months for the summer.  Jake was once again attached at the hip.  My son left again in August and Jake was sad, but not for as long and no stress pee this year. 

It is so hard to explain to the cat was is happening.  Just do your best to give her lots of extra attention.

Thank you so much!! That's very helpful. I've been giving her lots of attention today snd she seems to be getting on better. I will purchase those feliway diffusers as I have heard great things about them. Hopefully she'll adjust and get used to it quickly. Thanks again.