Surviving the Freezing Temps

This is our first winter with our alpacas and llamas and I'm having a hard time sleeping at night worried about them being comfortable in these freezing temps in Central PA. I'm sure that you've all been through many wicked winters and hoping that you can give me either some reassurance or suggestions for keeping these animals safe. I get it...the alpacas have inches of warm fleece and supposedly are equipped to handle freezing temps. I worry less about them than I do my 21 year old llama who is shivering like a leaf! We got a jacket for her and that seems to help a bit (it must make a big difference, right?). Not sure what the theory is on jackets? I've had a llama farmer of many years tell me that jackets are not necessary and can even be harmful, as it doesn't allow the llama to adjust to the winter. But adjust-schmajust...I can't stand to see her shivering! Well...even with the jacket on she is shivering away...so I had to step up my game and made a run to Tractor Supply and bought a heat light to hang over her stall. It's not like it makes it balmy in there...it just brings the temp up by about maybe 10 degrees? She hunkers down under the light every night and the shivering has stopped. Shwew. I have also started feeding her 2x/day, as she is quite thin. Per the advice of an experienced llama farmer, I added some senior equine feed to her grain. So she gets 16oz of food 2x/day. She has the option to get out of the wind, has hay to lay on, a jacket, a heat light and extra food. I'm one step away from bringing her into the kitchen for the remainder of the winter, lol. Too much? Is there something else I should consider? Attached is a pic of her at night...the alpacas are right outside a door that is just out of the camera's view. She has the freedom to join them or stay put. She stays put. I have a "not on my watch" mantra this first winter with the herd. Any advice is much appreciated!