Well if shes about 20 months she may be starting to get her 2nd year molars (if shes got her first already). That may be why she is not eating well at the moment.
My feeling is shes probably a little unsettled from her hospital stay, cold and possibly the new(ish) LO and wants a little more security from you.I honestly would try gradual removal.You have an advantage in that you are already out of the room.if possible stay until she has fallen asleep and try and move further away.
If thats not feasible then if you need to go off to attend to baby then just say something like "oh,i'm just getting a drink of water and then i'll be right back".that way she knows you will come back (believe me they understand an awful lot)
I know at this age i had to start limiting DDs nap to 2 hrs as it was impacting on her night sleep.so rather than add more awake time i'd limit the nap.if she short naps then do an earlier bedtime.
HTH