Just remember that people can be a bit fussy when it comes to their dogs. Just because she has offered you her customers doesn't mean that the customers will stay with you. People do seem to look up to more older groomers I find that alot, I own my own buisness and Im 19 so believe me with that issue.

How do you compare to qualifications? If she used to work as a vet people will see that as a added bonus, Knowing their dogs will be 110% dafe with this lady.

Can you afford the rent etc? What is customers do decide to go somewhere else? Why not see if you can do a partnership with this lady instead, giving her the option of a silent partner status rather than physically helping you.