GS is tricky, as I am a Leader also.
You are not allowed to sell, promote, solicite commercail products or host product parties for profit.
You are allowed to do things that the GIRLS themselves actually plan and run.
Depending on your council, usually there are limits as to what you can charge for profit. They want a serious plan with detailed specifics as to why you need the money, exactly what you are going to use it for, what are the girls going to learn ( planning, budgeting, marketing, leadership?) what part of a Journey/badge does the proposed plan benifit ?
Between now and May is pretty short time frame.
Are you looking for earning the full amount between now and then. Or just to fill in the gap ?
Things that come to mind :
Father Daughter Sweetheart dance. We just did a Father/daugher WinterWonderland Dance. We were allowed to charge a max of $5 per person. We provided snacks and refreshments. We purchased a cheap backdrop from Party City for $5 and had a picture taken of each dad/daughter. Prints were 9 cents each. We had 180 people attend. People paid in advance. We had about 3 couples show up at the door who wanted to attend, so they paid cash, which was fine.
Pancake Breakfast. Sell tickets in advance $5 aduts, $3 kids. We did a serving of 3 large pancakes for adults and 3 reg pancakes for kids, a side of breakfast sausage, OJ, milk, tea, etc. We sold over 120 tickets but only 50 some ppl showed up. We made over $500 for a few hours work. Some areas let you do things like this at Applebee's or Ruby Tuesday's/ Fatz Cafe. Our applebees lets you have a car wash in the parking lot at the same time.
Host a clinic/seminar. Look at requirements for younger girls badges. Have your girls host an event/ activity day for them to earn some of their requirements.
Paying in advance is the best way when you do any activity. When you apply for your fundraisers to council, make sure you let them know participants are paying in advance, this signigantly reduces your financial risk as your troop is paying nothing out of pocket up front .