Not sure where to start this but here i go... i think that it will be long

DH has a child from a previous relationship, he is now 9 (He lives with his mum the majority of the time) and we get along great, always have. He was the first person that we told about the pg and have tried to involve him in decisions and choices etc etc with his new brother or sister, whether he wants to change rooms, buying things and making sure that he is not feeling left out at all... he is so excited thou!

I didnt want his Mum to find out straight away about the pg (i was only 7 weeks when DSS was told) but she found out straight away... i was very very angry at this - whcih caused issues as DH stuck up for DSS saying that he was just excited etc (i now see this and realise i was being irrational, but was so annoyed that DH did not sympathise with me) but she can be very nasty and i didnt want her putting out any bad vibes and what happens if i had of lost it - she would have loved that (i know thats nasty of me to say, but she would have) - also DH hadnt even been told and i didnt think that last person in the world i wanted to know should know before our families.

DSS was sick a few months ago now, so i was still in my first trimester or maybe a week into my 2nd - it was thought to be a cold and as i was off work for a few days i agreed to look after him (she doesnt like taking sick leave for him - instead insisting that we must) on the thursday night he went back to her and she took him to the drs. The next day she rang and said that he was still too unwell to go to school and that we would have to look after him again - i pretty much refused to take time off work as i may need my sick leave form myself (and anyway as she is the main caregiver shouldnt she be taking sick leave instead of us???) She said that she couldnt take time off and didnt want him to go in with her to work as the DR thought that he may have the mumps or chicken pox!!! i was so annoyed, she didnt want to expose herself to this but was happy to do it to me and my unborn? I was P*ssed to say the least (this time DH was very very supportive)

Since then she has been fine(ish) when i speak to her, she asks how i am and takes glee in the fact that i am pileing on the weight. she seems nice enough to me and seems to be positive about it to DSS (which i guess was more of my fear - that she would be horrid and fill his head with negatives about a baby bro/sis)
I have not seen her since being pg as i dont want to - i didnt always see her anyway.

Right now down to the business end - i really want DSS to come in very soon after i have given birth to meet his new Bro/sis BUT i am terrified she will want to come in too - she wanted to come to our wedding years ago and threatened not to let DSS be a part of it unless she came (it all worked out in the end - only because she had something on!)

i dont want her to have anything to do with my child - i far from agree with her parenting and i dont really like her to be honest, she uses her child to benefit her and i dont believe that she has his best interests at heart (but thats another story). I feel that just becasue i am involved in her sons life does not give her the right to be involved in my childs...

I have always tried to maintain a nice situation between us as i do not feel that it is going to be in DSS benefit to have obvious nastiness (not that it stops her being nasty about us to him though) I am always pleasent to her (except maybe one time that she told me really nasty things about DH when they were together and then expected me to break up with him/call off the engagement)

I have noticed that since i have become pg, i am resenting her more and more and as such at times am overly picky towards DSS(especailly if its anythig to do with his mum) - which i hate as i really love him as if he was my own (well as far as i know) and want only the best for him.

Has anyone else been in a similar situation?
Am i over reacting?

thanks for reading!