I doubt it's real suede Lonie. Seat cover or scatter cushion? Either way, unzip the cover and look for the label just inside which will tell you if it's washable.
I appreciate you may not have time to do a full wash on it, but scrape off any excess, rub a lttle vaseline in to loosen it or (chancey) meths. You could rub in a little washing machine liquid and then launder.
Or it could be a dry cleaning job.
Or (sneaky) get hold of your mums lippy, add a little to the stain, say nothing. This is reliant on lippy wearing mum actually ever going near said cushion.....
I'm not usually this devious, but I guess you need different options....
Best option - tell her. She'd prefer to deal with the stain herself ......