Hi Missedcall
Firstly - how old is your DD?
And are you 100% sure she's not allergic to hay (they must have) or fur ( my DD is allergic to one of ours)
Are you prepared that you will be doing alot of the work? Even if your DD is on board which I don;t doubt, it's too much for a child. And legally, if your DC are under 16, they are yours .
Bedroom - no.
Many Rescues (I don;t know where you plan to get yours from) won't allow pigs in a childs bedroom. Too warm. Usually not enough space.
They can be quite noisy (not in a nocturnal way but just day-to-day)
And their hay smells. I put ours in the small bedroom at 5pm and already the hay is making itself known.
Think about what size of accomodation, and ask yourself honestly if you have the space indoors. They are happier in a family room really.
(There's a website on C&C cage that gives sizes, but bigger is better)
Storage of hay, bedding, newspapers, their dirty bedding till your bins get emptied.
Outside they need a safe , protected hutch . Protect against weather, foxes, cats, heat, draughts and damp.
Safe run that you can move about.
Boars or sows?
Sows are easier TBH but they can be grumpy and territorial - not all guineas will get along, like people. (Our 2 sows aren't related but get on well.)
Boars are lovely but need space and will go through a 'Terrible Teens' at 3-6 months. Don't trust people who say they need to live alone ( they don't) or they need neutered (they don't, unless you want boar/sow)
Always a pair or more.
2 or more sows
2 boars (fine if there are no sows)
A neutered boar with as many sows as you like but only one boar in a group.
Where are you planning to get them and what age are you looking for?
If you want boars, go for the biggest accomodation you can.
You need to make sure you get them properly sexed.
And hope that if you get sows they haven't already got pg (I bought a pg sow years ago) and I despair when I see adverts (Gumtree grrr ) "I have 8 guineas, boys and girls, all 8 weeks," all together, they could already be pg.
DD wanted a guinea boar, we got 2 rescue 1 year old brothers. Total love sponges, loved people. They had a scrappy period the first winter but it was sorted.
When one died, we got a tiny male piglet (Rescue) so my DD got her baby guinea.
When the older one died, we got the 2 sows (Rescue) and kept the boar apart from them while he was neutered and went sterile then they were introduced.
They are lovely. I love the sows though the boar has a real big bolshy Boris Johnson air to him.
He's also the one that DD is allergic to.
Smooth coats IMO (others might not agree) have fewer health problems.
One of our boys was an Abby (rosettes) they have shorter noses and can get cataracts.
Our currant boar is Rex (short wiry coat) they are big (he's 3lb) big feet, and the fur that brings DD out in a rash.
Girls are smooth.
Any questions, feel free. Lots of guinea - slaves here 
Not trying to put you off, but it's as well to know the ins and outs beforehand.