Ive been hypothyroid since before the age of 10 (im 25 now).
My cycles are "regular" but not down to a day or anything like that (32-35 day cycles depending on ov. which rarely happens on the same CD, usually CD 22-25). And i only have 10 day LP, which is bare minimum. I know my thyroid is playing into this but based on a ton of reading i actually think that is because i have an estrogen dominance and a progesterone deficiency, which can make thyroid not function properly. Even when my thyroid is being regulated with meds (which it always is), i still have those issues. So anyways i could have more than thyroid going on but so far my experience has been this:
baby #1. Got pregnant first cycle. Sadly MCed.
baby #2, healthy baby boy, got pregnant first cycle.
baby #3, healthy baby boy, got pregnant after 7 cycles.
baby #4, pregnant with a girl after 7 cycles.
Now the biggest issue i have had, personally, has been during the postpartum period. There is a condition called "Postpartum Thyroiditis". As established i have been hypothyroid since a very young age (not Hashimotos though). PP Thyroiditis can present in a few ways, but mine personally goes super hyper around 2 months PP and then super super hypo around 5 months PP. This has happened both times ive been PP. I presume the same will occur. It causes a TON of symptoms. The hyper state is the worst. I feel im running a rage, im emotional, mean, moody, bitchy, i get the jitters so much i feel like i must be withdrawling from meth. Then when i go hypo i get all of the classic underactive thyroid symptoms but i go reallllyyyy really hypo. After DS1, my thyroid went from .001 (thats about as hyper as you can get!) to 12.59
i gained 35lbs in less than 10 days-no lie. It literally changed overnight. Then after we get the thyroid med levels figured out, which takes a lot of bloodwork and adjusting, im on thyroid meds for life. (much like prior to my pregnancys). My thyroid, without meds, is in a constant state of hypo (the meds fix it if on the proper dosages, but i never go hyper, outside of PP thryoiditis)
So for me, i am sure that it causes some fertility issues (i also have endometriosis too). I def know that thyroid is a very very important function when getting and maintaining a pregnancy too. So it can def effect badly to getting pregnant.
One thing that is kind of indirectly fertility related, is that i have a condition known as Insufficient Glandular Tissue. This means i cannot ever EBF bc i lack the glands, tissues, and milk making factory to produce enough milk. I firmly believe that this was caused bc my thyroid went untreated during puberty. (you cant grow breast tissue well with low thyroid and low progesterone-they are two highly important hormones, amongst others, needed for breast development). So even though that isn't an issue with actually getting pregnant, it did cause other reproductive issues for me. And if it did that to me, im totally sure it can do negatives to actually getting pregnant.
Anyways, if she is taking meds and getting her thyroid checked frequently (to make sure she is on the proper dosage), then once he blood reveals normal levels then she should be able to concieve, assuming that is her only issue. Essentially while taking the meds gives off same function as someone who doesn't have a thyroid disorder.
If i would have waited for my thyroid to work properly, we never would have had children since its been that way pretty much my entire life.
hee hee. 
