Well I did not think this game would have incest with MC, so it is very unlikely. Besides overall neither MC or Emily are strongly setup as being interested in each other sexually or having a strong reason for themselves to want a relation like that, so I would say it was never intended as such either. The only two ways to add it in somewhat believable would indeed be give Emily a surprise turn of character and have her sexually perving already in such a way without mc or players knowing it as described or her trying to use her sex appeal to keep MC from leaving her if she would really get afraid of losing him. Neither fit with her as shown into game though, she seems to be overall a pretty kk character that has her own life, a support network and not obsessed with her son, but just loves him in a normal way.
I do not see either one happening though, MC has already enough problems without his nice mom turning into an obsessive sexual predator for him. He already has Erryn for that.