My 10 year old cat keeps throwing up spit or yellow foam.?

[AerithGainsboroughe]

I just recently got a kitten and brought her home on September 17th. My older cat Storm, who is 10, Doesn't seem to be very happy with this. They sniff each other, the little one loves Storm but Storm doesn't have that playful energy side to her anymore. She's been throwing up a lot, everyday. Sometimes it's just clear liquid or other times white or yellow foam. I'm really worried about her, and don't have the money for a vet right now. Is this just stress doing this to her? Will she get better? Thank you so much for any information.