Squidley, welcome to HealingWell.
I don't have Hashi's, but we do have several posters who do have it. Basically, it means her immune system is attacking and neutralizing either the thyroid gland or the hormones produced by it. This makes her hypothyroid and yes, this can cause low energy as well as other symptoms - dry skin and hair, muscle and joint aches and pains, inability to tolerate cold and feeling cold all the time. For more information on hypothyroid symptoms, you may want to review the "Thyroid Basics" thread here (just click on the colored text to see it:
It certainly is treatable, in most cases relatively easily. It can take some time to get medication adjusted properly, and be prepared for it to take about six weeks for medication changes to take full effect. Good luck to her.