Not to want to suprise 90yr old for birthday.

Surely the party girl will want her hair done and to look her best? She needs some sort of forewarning even if the precise nature of the event isn’t spelled out, and her GD is probably the person to do this.

I don't see why your daughter shouldn't 'be in town' and visit her grandmother as she normally would. As long as she doesn't let on about the surprise party, I don't see that SiL has any right to complain about that.

I agree with MamaCaz - she is here for a visit and it seems mean to not spend some time with her grandmother. They will enjoy the sort of conversation that you can’t have at a party.

I know you could argue that they can have this quiet chat after, but sometimes a party takes a lot out of an older person and it will certainly not be the same.

If she doesn’t mention the party there’s nothing to complain about.

I think a total surprise party is quite a risky thing. Who knows what this lady really wants to do?
My sister in law wanted a big flash hotel do for her mum's 90th local to where they both live, but mum said no as lots of us had to travel and the costs would have been unreasonable.
I tried to organise my own 60th birthday party meal for friends and was put off at every turn as dates didn't suit etc. Turned out they'd organised a surprise, but not something I would enjoy, which one friend freely acknowledged but said it was what everyone else wanted to do, and at a restaurant she knew I didn't like but other people did. So I went along with it but felt really out of things and could have cried.
I had my preferred meal out with my son later and had a lovely evening.
Personally I feel the venue and type of party is something the birthday person should be involved with discussing. There's always something else that can be a surprise on the day.

We had a surprise birthday party for my 80 year old aunt and she just seemed bewildered all day . Far better that she knows in advance.

My mum had a 90th. She helped plan it, said who she wanted there, had a new outfit and her hair done. Does your SIL not realise for someone that age the anticipation, the planning and the preparation are half the fun? Not to mention looking your best on the day. If my mum had been surprised and hadn't had her hair done properly or perhaps not rested during the day so she wasn't tired at night she wouldn't have enjoyed it half as much. As it was she stayed until the very last guest was ready to leave. It's fine to plan small surprises but older people need to be ready for big events.

Thanks everyone. I talked to my daughter yesterday, and even though we both are not fond of surprises (especially for elderly) we will go along with my SIL's plan.

I know my MIL will be delighted with everyone coming to see her. She knows SIL is coming into town and there will be a family dinner, but does not realize granchildren and great grandchildren are also coming. Hopefully she will be delighted but not overwhelmed.

Personally I would hate it.
Please ask SIL if she will at least warn her Mum to dress up and get her hair done because 'you should expect visitors on your birthday'.
If anyone organised a surprise party for me I would go home, or if incapable of physically going home without help, I would get really furious and refuse to co-operate. (ie I'd sulk)!!!
Although to be fair - SIL should know what her mum is like and whether she will love it or hate it. After all, she IS her daughter.
It needs discussing.