Hi fin female platy quiet at top of tank

[Ciccio12]

Hi all I'm quite new to this fish keeping. Approx 12 months. Had a happy and healthy tank for a good 6 months now so decided to add some new recruits. I purchased 4 platys. 1 male and 3 female. Only had them since Friday. Noticed yesterday one of the females has a rather large tummy and today she has now gone into hiding at the top corner of the tank. Just wondered if there is anybody who could say this is normal behaviour and if she is pregnant or not. The other females haven't got the large stomach and are buzzing around as normal. Thanks. I've added two pictures...

 

[fish48]

There are a number of reasons why she may have gone into hiding, sometimes females go into hiding just before their due to drop their fry. it probably is pregnant also a fat tummy can also indicate she's eating lots of food. I think the fish in the pic looks more like a Sword tail and not a HI fin type .