This thread has made me laugh. I work in the tourism sector. For a group booking, most if not all hotels for that many rooms, will have a breakdown of the cost of each room. For example, the cost of the larger room accommodating four people will always be more expensive because of the linen charges. However, as an example, the cost is £145 per night for the room, the cost should be divided by four people which will always work out cheaper than the cost of a double or twin room. Our site handles a lot of group bookings and we recommend to the booker that their confirmation email does (and it should have for tax purposes) contain a breakdown for each room.
It appears the booker has got the total cost and split it across the amount of people going. In fairness, that would be fine were all to have a room each.
I would ask for the breakdown of the room costs and those assigned to each room split the cost equally between However many people are sharing the room. Ultimately, that will mean some people are paying more, or the organiser says, this hotel looks good, all book individually.
It is a skill organising a group event, we have them regularly, usually with corporate travel agents, however, we have a regular group that come twice a year and they all have single occupancy and all pay the same for DBB. But in double rooms as that is what they prefer. For events, eg hen and stags, it is usually people booking individually.
I do feel your organiser has poorly planned this as it won't be just you feeling it is unfairly mapped out. Have a private word and ask the terms and conditions of the booking. Has a deposit been paid ? Usually would be for a group booking unless she has booked through say booking.com,that would then bring its own set of problems as that would have to negotiated through that channel as the hotel would not be able to make changes to the booking.
Have a private if you want to preserve the relationship and support her. If you drop out, that will then increase the cost to the group, so you're landed with another problem then.
If people are paying for a service then it should be open & transparent, the cost of each room will be on the booking confirmation.