beatrice25

There aren't really special rules for minors here.
A single trip under 12 months is unlikely to be an issue. Multiple extended trips outside of the country can become an issue.
Once somebody passes 12 months abroud, there is a presumption that permanent residence was abandoned.
 
A re-entry permit allows staying abroad for up to 2 years at a time without the time alone being being a basis for determining permanent residence was abandoned.
That said, a re-entry permit would only be valid for up to the end of their existing green card's validity, since it is under 2 years already (as a conditional resident). So it may not have any real value here depending on the actual timeline.

I sent my daughter back to Philippines while she has conditional green card. She stayed over 2yrs. I became USC I just filed i130. No issue, its already approved just waiting for NVC to schedule interview appointment 

Yes, refiling is another option, assuming they can still sponsor them (due to finances, age, etc.).
But I think the OP's focus was on retaining their permanent residency status.

Hi! Just wanna share my experience.
I scheduled my medical 1 week after I received my MNL number (July 22 and 25) and my interview a week after medical (August 1.)
July 19, I had flu. I cannot get up without feeling dizzy. I was coughing and sneezing badly. I opted not to take medicines. I tried to drink milk, but it made the coughing worse. I tried drinking pure ginger tea. My condition got better, but I still had chesty, dry cough. I thought of rescheduling both medical and interview then I chanced upon this thread.
Anyway, I went ahead with the planned date. I was coughing hard inside SLEC. I thought it was the end of me! Being a bit defensive (and paranoid) I talked to the radiologist and explained my common cough. I immediately had regrets after that when I remembered Greenbaum's message "Do not volunteer information."
So there, I spent the whole weekend worrying and planning and exaggerating things in my head. When I came back this morning, I was instructed to proceed to immunization. XRAY is clear. Thank God

Hi!
If you want to save on shipping cost, check the requirements and consider sending only the documents that will need your wet signature. She can prepare those that doesn't require to be original or doesn't need your wet signature and the 75 pounds of Evidence of Genuine Engagement here in the Philippines.
I just got approved last Monday. For our Evidence of Genuine Engagement, I included a picture for every place we visited, one monthly screenshot of FaceTime and chat log in the last two years. I also included passport stamps and visa and hotel bookings. I printed everything out and it was 150 pages in total- just for the Evidence of Genuine Engagement. I have a little OC tendency lol. The CO officers in Manila Embassy did not look at the entire150 pages. They just scanned and checked probably 5 pages.
Just send her the following:
1.NVC letter (I read some just printing out the the CEAC website)
2. Affidavit of Support, which includes your 1040, w2, recent pay stubs, certificate of employment and bank certificate. It is in the packet 3 requirement, but the consular officer did not ask for it during my interview. However, I heard some COs asking for it.
3. Proof of termination of prior marriage, if applicable.
4. Also, send an updated intent to marry and a copy of the bio page of your passport (Not required, I just want to be prepared. My OC tendency.)