Worried

[Cherrypies]

About one of my cats, going to contact the vet, but wondered if anyone has any experiences of the problem.
She is about 6 years old, ex feral.
On Thursday, she vomited a quite large pile of sick, brown and lumpy, with an absolutely foul stink. She was fine the rest of the day, eating ok.
Last night, she was lying on the carpet, and must have farted, foul smell again, also miaowed loudly, I thought she had diarrhoea, but the carpet was clean. Still eating, still purring, and responding to strokes.
She is lying down now, and she has just cried again, no foul smell this time.
She has eaten tonight eyes are bright and clear.
She is long haired, could be a hair ball.
Any thoughts?
Thank you