Good Grief! DON'T add the potty training dilemma to her surgery! Poor thing! DON'T use panties! DON'T overload her with drinks! DON'T do this thing!
I get it that you are frustrated, but imagine HER frustration! She doesn't talk yet, she has been in pain in her short life, thus the need for the tubes.
Put her in the new 'pull up' type of diaper that comes off easily & then put larger panties that are tight but still comfy over them & keep an extra eye on her (you will be doing this anyway since the post surgery will be a time for caution).
She will come around to the potty on her own time, give her a break mama!
I have just read over ALL the other responses & I can say I am not a newbie to this dilemma I am 59 & raised 4 & now am raising 3 again, sooooo I AM saying ALL children are different you CANNOT lump them into categories, by saying, '20 months-2yrs-3yrs' each individual child WILL come to potty on THEIR own terms! I have raised children who were COMPLETELY trained by 14mts. all the way to 3yrs.!!!
Your little one has communication problems, she is just as frustrated as you are, she NEEDS the space & time to, 'get it'.
Hoping for a speedy recovery & a wakening to sound for her & your family!