Waking Up Wet

Have you thought about changing her nappy in the night? 

If your daughter sleeps soundly enough you'll be able to change her in the night while she's still sleeping.  My son (aged 2) has had an occasional dirty nappy in the night which I've discovered when going in

I wouldn't recommend putting another bigger nappy on over the top, because if the first nappy is leaking out the top or sides the bigger nappy on top won't really catch the wet.  The only way a bigger nappy over the top would catch wet is if the smaller one underneath was actually leaking through the front or bottom. 

I've always thought Huggies were the best brand to stop leakage of both wet and dirty nappies, but you don't say what brand you're using so you may aready be using them.