the reason for her hiding in the tank is due to the fact you have a male molly (?) in there and she is being hounded like crazy to mate again and again.
its really a hard thing to answer when it comes to breeding net etc...
it does slightly stress your fish out but it is highly possible that she will go full term and give birth in there.......................i know that this will generate a few negative responses but...if you want to use a breeding net then you use one, you have a mind of your own, just keep a close eye on her, as soon as she drops her fry remove her,she may well drop more in the tank afterwards but this will be a good natural way of controling the amount of mollies you end up with and as you will soon realise they breed like crazy.
try not to be put off by the way some members reply to your questions as sometimes they do sound a little harsh when read but its not intended. its like reading a text,you never know wot the intention of the text is as its hard to see any emotion in them.
as for lying at the bottom, she is close to giving birth as yes most fish do this
good luck with her and remember that you are here to seek advice on the question you ask not wot people think they should be telling you
regards