We have two DD's, now aged 9 and 6.
They both began camping when they were 4 months and have loved it ever since.
They make sleeping bags for little ones that have the blow-up mattress attached. Our girls used theirs when "camping" at grandma and grandpas house until they outgrew the mattress. Now, they have a camping cot that they use since she won't put them upstairs by themselves.
If that doesn't work or if you can't find one, just use a sleeping bag. When kids are that age, they can sleep on anything.
Put them to bed in your room and let them lay on the floor while you lay on the bed and then after she goes to sleep, enjoy the evening.
Make sure she gets plenty of sleep since she will be going (and you will too) from daylight until whenever.