I would never kiss while on the hobby. My greatest fear is if she has been doing BBBJ on the last guy ( or her BF ) You may be tasting another guys DNA
No offense, but I think your greatest fear should be bear attacks or tsunamis.
Unless you and the last guy (or her BF) are in a threesome with her and that person finished in her mouth or she answers the door with a mouthful of something, the chances of getting something from a previous client while kissing her I would say are pretty negligible.
I would guess all providers who perform cim will
a) rinse
b) drink something
c) swallow their own saliva many many times
d) possibly eat something
before seeing the next client.
If you don't think she's doing that I'd say you shouldn't be visiting her because she's likely not following other basic hygiene.