She’s a keeper
Nice bday gift, one of my favorite corals. They are actually super easy if you just dedicate a few mins a week to them. I took a single fat head and turned it into a colony of 35+ heads in 2 years by spot feeding it mysis and reef roids 2 to 3 times a week. Your colony is already open during the day which is half the battle. I had to start feedings at night then slowly move them till it would stay open during the day. Be careful if you go on vacation for more than a week bc they'll start to close up from not being fed. Also be mindful of hermits, starfish and shrimp bc they may steal the food right from them. I would also relocate the colony to a semi shaded area with moderate flow off the sand bed to make it more difficult for other creatures to steal its food and easier for the dendro to grab any food suspended in the water column. The more you feed the faster they will grow.
Anything that is meaty and on the smaller side will do. You'd be surprised at how large the pieces of food the dendro can consume. Soaking it in selcon or another supplement is always a good idea, especially with frozen brine. Hikiari mysis is on the smaller side, PE mysis is the larger one.
