First time bearded dragon owner struggling with baby bearded dragon

Hello! I am a first time bearded dragon owner, we have had our baby bearded dragon for almost two weeks now. I have tried holding her (she's around three months old so who knows her gender), and while I can for a bit, she always gets those black lines, which I read is stress. Even when feeding with tweezers she gets stressed. She ate around 20 dubia roaches yesterday, but today she seems uninterested. She seems to be eating enough to survive (not consistent), but not the healthy amount. She is basking a lot but we just cant figure out a way to have her at least tolerate us? Is there anything we should do? Just for information sake: She's in a 40 gallon right now, when she gets bigger we will move her to a 120. Her basking spot stays around 110, cooler side of the enclosure is about 75 degrees, plenty of places to hide. She doesn't seem to go anywhere but her basking spot or cave at night. The other side might be too cool. She has UVB and UVA/heatlamp. I know that it takes them awhile for them to settle in. We are just not making any progress with her. And we are concerned because she is not eating consistently, although pooping regularly.