To tell or not to tell?

So my husband and I have been TTC our first since July with no luck so far. We haven't told anyone (unless you count me talking to our puppy) that we are even trying at this point.

My sister just told me that she is expecting and due this May. Do I tell her that we are TTC? Backstory...this is the same sister who threw a fit when my husband and I got married 2.5 months after she did because we "stole her thunder".

I even considered taking a break from TTC for a few months because of this, but then I think - why should I put my life and family on hold just to avoid her being upset?

I would really appreciate your advice, especially if anyone has gone through something similar. Thanks in advance!