Back in April..."average" gestation period for a RES is two months but all are not alike some even three months. Females also can hold sperm for several years until she's ready. She could just be gravid / infertile.
Good read :
http://redearslider.com/reproduction.htmlNot eating is normal , she may fast a few weeks before eggs are laid. Partly to allow room for eggs to grow and may just feel bad. Does she look for a specific food , also may reject a lot of others. Attention to diet is a must , what she may prefer , so it's available to her.
Home made nesting boxes normally do not work. Most of us use our backyard gardens for them to lay. Must offer her place to lay eggs fertile or not , her holding them and eggs binding can kill her.