Well, I'm curious: what IS your 'timetable' for marriage? Not necessarily with her, but in general.
The only reason I ask is b/c it seems to me that older people usually know very quickly whether they have found their life partner or not. From that perspective, 5 months is plenty of time for people who know they've found what they have been looking for.
I suspect your feelings are more a muddle of your issues from your previous marriage and her not being quite the right fit for you. Also, she would have had her daughter at 36, right? That's getting up there for a woman. Is it possible she got pregnant in order to try to trap the father into marriage? That could be a source of her desperation.
Ultimately, she wants marriage. You need to decide if you do also. If not, you ARE wasting her time if that is her goal and you should let her go. Its only fair. This is completely separate from how she is handling it, tho yes, it is an indication of how you can expect her to handle other problems in your relationship.
Tough choice, good luck.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh