Quest Thermolite - junk or OK?

[TauPhi111]

Going on my first backpacking hunt this year and I'm planning on borrowing my girlfriend's sleeping bag for my first time out. She supposedly has a Quest Thermolite -10 bag. I haven't seen this thing yet, and I don't know much about the brand other than it is inexpensive compared to what people on here usually talk about, so I am a bit apprehensive about quality and performance. What I'd like to know is whether I'm going to freeze my ass off or not in Southwest CO during 3rd rifle or not, and if it is going to take up half the space in my pack. For this first outing, I'm not really worried about the weight of the bag since there is a lot of other gear I don't have/need yet (like a spotting scope, bunch of elk calls, etc) that'll save me some weight til next year. Will this keep me warm at night, or should I buy something better right away?