Bless you, what a tough thing to go through and such a horrible time. I'm so sorry for your loss of your little girl.
Are you getting additional MH support through this current pregnancy? I can imagine it's pretty draining.
I would say, don't beat yourself up about your current feelings. You had been pregnant long enough with your daughter to be picturing life with her and daydreaming about what having a little girl would be like etc. You then had that ripped away. I guess when you fell pregnant again, part of you sort of picked up where you'd had to leave off, and then finding out it's a different future you are now facing is sort of unsettling and new.
I had three losses myself last year - all first trimester though so no idea 'who' I lost, however I am now into third trimester with my second little boy and I did have a moment of 'I wonder if any of my losses were girls' - especially when looking at baby clothes etc. I can imagine that actually having pictured that life more would make it all more complex to process.
It doesn't make you a bad person to be feeling saddened by that. What I would say though is that, even if this was another girl, you wouldn't be getting back what you'd lost. Sadly, and I guess this is where processing the grief comes in, your first little baby wasn't for this world, and even if you were now expecting another girl, she could have been completely different to her sister.
I'm not sure what your beliefs are around death/loss etc but I wonder if it would help to think of your little girl sending this little chap to you because she knows he is actually what you need right now.
If it's any comfort, I promise you, you will love your son so much when he is here. I absolutely adore my little guy and I'm genuinely excited to have another boy on the way. My son (now 3) brings me so much joy, gives the best cuddles, adores his Mum, tells the cutest/funniest stories and just fills my heart with gladness every day.
Go gently on yourself. Remember you are still on the depths of grief whilst also navigating the joy and nerves that a new pregnancy brings. It's ok to mourn the life you're not getting, but give yourself space to feel excited about this new future too. It's not dishonouring your daughter to get excited about a new future without her in it. And it's not dishonouring your son to have moments of great sadness that the new future is one without her in it either. 💗
Sending you lots of love and best wishes for the future 💕