How can I describe lips which are wearing lipstick?

Not a very common word, I’d say, but the easiest and most obvious choice would be to simply turn ‘lipstick’ into a verb through zero-derivation, and then using the past participle of that verb:

Her lipsticked lips were pursed.

Googling “lipsticked lips” yields about 15,000 hits, which isn’t much, but enough to show that this word has been invented and used before. More tellingly, the OED has a subentry for it as well.

(Google also reveals that I am not the first to have thought quippingly that the past participle of ‘to lipstick’ really ought to be lipstuck. I’d not suggest using that, though.)

Plenty of writers (7000 of them in Google Books) have referred to...

her rouged lips (rouge - a red or pink cosmetic for coloring the cheeks or lips)