Being the boss blues

This whole pregnant emplyee thing is really tough.  I see myself blogging a lot about it for a while.  Here is my new dilema.  So, this gal who is pregnant is my worst employee.  I don't mean it because she is pregnant.  Before I left for the buying trip overseas, I had started to reprimand her for the incredible amount of mistakes she was making.  She is a serious space cadet.  I run a crystal new age shop so it's pretty laid back and openminded.  Honestly if you came to work high, did your job well and i never knew, I wouldn't care.  But this was not the case with her.  I had to tell her not to smoke while at work, even on breaks.  She is wonderful with customers and has a lot of knowledge about all this new age stuff.  But she can't get it right on the register to save her life.  I have tried everything to help her out.  I believe that everyone brings something special to the store and I try to help people cultivate that and overlook some of their flaws.  But this one was getting bad.  Money mistakes meant the store was just losing money.  But she is always willing to be at work as well.  So when I was getting ready to leave for the trip, I put off any serious probation for her until I got back.  I just needed everyone there and happy while i was gone.  But bam!  When I get back she tells me she is pregnant.  Great.  Now I'm in a shitty situation.  For the past few days she has been feeling sick at work and going home, not doing her share of the "chores", and continuing to make register mistakes.  But now I'm afraid i feel extra annoyed by this all because i am annoyed that she is pregnant and I am resenting her.  I'm worried that that may be true and others will think it is.  I feel like it will look like I am punishing her for being pregnant.  Who yells at a pregnant girl or even worse have to let her go?  I had an empoyee a few years ago get pregnant and have her baby.  It was right before we started trying and I was more than happy to bend over backwards to help her.  But she was my best person on the job.  She didn't want any special treatment and worked sometimes until I would make her go home.  Ugh.  I know a little part is the jealousy.  But now I just feel confused how much is my feelings and the truth.