If she has a basement beneath that dome holding a lot of equipment, yes.
She'll need equipment to do electrolysis to split water into hydrogen and oxygen, so she can breathe. She'll also probably need some kind of furnace, in which she can burn kelp or other plant matter. This is because the tree and grass probably need more CO2 than can be provided by one squirrel. I highly doubt she and the tree are in perfect CO2-O2 equilibrium. She'll need desalination equipment to get fresh water. Pressure is no issue. Submarines regularly dive much deeper. It won't be all that cold, so heating is not too much of an issue. Temperature varies a lot as the ocean currents change, but it will generally be about ~60F or ~20C at that depth. She can get food with hydroponics and grow lights. All of this will require electricity, so she'll need some kind of power generation; maybe geothermal or nuclear. Fossil fuels don't work because she needs the oxygen.
At 55m depth, there will still be some light, but I don't know if it is enough to keep grass and an oak tree alive. It will be approximately 25% of the light on the surface. I suppose she could use more grow lights, but we don't see them when we look at the dome.