Hi just looking for some advice

My 5month old shih tzu puppy got groomed 2days ago since coming back she was very tired and larthargic which is unusual for her. The tiredness has been constant even her not barking in the morning (out of the ordinary) she has since vomited and hasn't ate since beig groomed. The vomit looked like a treat given to her and she has also done a very watery poo too.

She is normally very hyper active and fun loving but she seems like a different dog. Should I take her the vet?

Yes, she could have parvo.

If your pup is that noticeably not herself a trip to the vet is in her best interest. It could be a number of things from colitis, to having gotten into something she shouldn't have, like tables scraps or trash to more serious things like an obstruction or parvo.
Are there any chemicals around that she may have been exposed to, either in the house or lawn sprays?
I would take her in soon, being a small dog she can't vomit and have diarrhea for very long without becoming dehydrated.