Honestly... you shouldn't have nursed her when she was sick b/c you now have to "break" two behavioral patterns again instead of one. We had to "referberize" my son after a bout with the flu and it was tougher the second time around b/c he was older and had more stamina (10 months vs. 4 months). For my son, it wasn't about the nursing so much as sleeping with me... when he was so sick and up all night my husband and I took turns sleeping with him on the guest bed which he loved.
Stick with it, don't cave in and keep the method consistent. There is no nutritional need for a toddler to nurse in the middle of the night. She's looking to be soothed back to sleep, which is something she needs to be able to do herself!
She's older now and "gets it"... if I cry they will come to me (by "they" I mean you and your nursing). It will take longer to get back on track, but you won't have to do this every time she gets sick. Just the first time... once she learns to calm herself, you'll be fine and sleeping once again!