I've left my kids several times--the first being when my oldest was six weeks. Sometimes it's been just a night or a weekend; last year (when my youngest was five months), we left for seven days to visit Canada. Either my mom or my stepmom always take care of the kids, so I know they're safe. In fact, my "moms" actually seem to be more attentive than I am to my kids!
I never had any issues with thinking my kids were going to forget me cuz I knew they wouldn't (and neither will your daughter). However, I definitely made a lot of preparations to be sure their time with Grandma would be pleasant, and I wouldn't have to worry while I was away. I agree with the other mom who suggested having your mom come over so you can show her the basics. Maybe have her over for dinner one night if you can, and then she can participate in putting your daugther to bed. It would also be a good time to show her how to dispense any medication, apply diaper rash cream, feed her, etc.--basically, anything that she'll need to do for your daughter while you're away.
Also, be sure and leave a signed (preferably notarized) medical authorization giving your mom permission to seek any necessary medical attention in your absense. I had a friend of mine who is an attory write mine up. Shoot me an message w/your email address if you want a sample.
I've also always left a detailed note for the Grandmas, even though they've taken care of the kids before. It includes everything about the kids' day from what to expect when they wake up, to when they take naps, to bedtime routines and any important "tricks" I use to help calm the kids. I also include information about taking care of the house, how to work the TV, when the yard guys might come, etc. I also include directions to the nearest minor emergency clinic, their pediatrician's office, the nearest ER, and the nearest "fun" places my mom might want to take the kids (even if it's just Sonic so she can get out of the house a little and not go so stir crazy).
There's a lot to be said for being prepared, and it'll definitely help you be able to relax and have fun. As everyone's said, that's extremely important for you and your husband. Good for you for taking some time to yourself. You'll be a better mom for it!