I would say it's OK but would perhaps wait for DSD to invite you. Or if she talks about a play ask her if she'd like you to come - because you'd love to see her. Of course if your DP goes it's fine to go with him.
I actually go to everything my DSS' are involved in - sometimes instead of DH if work gets in his way! (he owns his company so it's not often btw).
DSS1 lives with us, DSS2 does 50:50. DS & DSS 1 &2 all go to the same village primary. I pick DSS2 up with the other 2 on a Friday and drop them all off on a Monday so I am involved in his school, they also know me because of DS. I attend class plays, parents evenings etc. DS and DSS1 are the same year and same class at school because it's 1 form entry.
I/We just make sure lines of communications are always open. For example school reports came home last week. We get a copy of all 3 boys and DSS' mum gets a copy of both her boys.
This week was end of year parents evening. I have DD (5 weeks) and 14 month old twin DS'. I am not up to doing parents evening. DH went with his DXW and they saw their boys teachers. The teacher then moved onto discussing DS and his DXW suddenly said - 'oh I think I should wait outside'. My DH just laughed and said I wouldn't mind and that she probably knew it all anyway from their boys! (she did go out btw!)
Sorry, the whole post comes across about me and my situation but what I wanted to show is it can work. We are lucky enough to have truely blended - we work as a team of 3 people (actually we're expanding as she now has a DP with a DD the same age as the 2 oldest boys!).
We just work on a best for the children, who can be there for them bases as oppossed to who it is that actually attends. A few weeks ago I couldn't move (post birth!) DH had to go away for the night (business/ large contract I didn't want the family to lose the money) so my DFather attended the boys assembly. All 3 boys were fine with that - they all love him and to them all he's grandad.
As I'm the one on maternity and DH, DXW and her DP work so most daytime things I do.
I agree 100% with exotic It is a shame when people don't see the benefits of all the parents just the negatives and one up manship.