I'm brainstorming here, so some of these ideas might not be applicable if they break any organization's (including HubPages) rules. Please know that I'm showing good faith here and may be ignorant about certain protocol.
1) Most churches have "sister" churches. Have the girls draft a generic letter soliciting help from these affiliate churches.
2) Similarly, does your church fall under the umbrella of a church conference? A call to the conference office might prove beneficial in terms of finding a special fund that could help augment the funds already gleaned.
3) Do the girls have any special talents? Are they effective public speakers? Help them plan a one hour program. If they lack talent, have them organize those who do, ask a civic group or your church for an evening's free rental of a large hall, and either charge inexpensive admission or ask for a freewill offering that will go towards that trip.
4) You're an established Hubber. Write a press release announcing the mission trip and ask for free publication and air time from your local media organizations.
5) If HP allows it, write a special Hub and include a link where fellow Hubbers and other browsers can donate unspecified amounts. Include a chart, if possible, that is continually updated so people can see at a glance how much more the girls need.
6) Bake sales, rummage sales, yard sales.
7) Get on eBay and start selling! (I'm user id snugchat and can offer limited mentorship if you contact me directly through eBay.)
I hope these ideas either help or get your creative juices flowing. Suggestion: Write a pre-trip Hub and a post-trip Hub!