Milk goiter??

I take it she is still nursing?

Weaned 2 weeks ago

Could be iodine deficiency . You can test her by painting 7% iodine on her tail web, where there is no hair. If she absorbs it the she is needing more iodine in her diet. A Milk goiter would be in place before weening and slowly goes away when weened.

I just bought her last night from a friend so not sure when it came up. Where can I find iodine?

Ok told you wrong. Weaned off mom 2 weeks ago but was given milk replacement until I took her home last night.

you can get iodine at tractor supply

Lump has gotten a little bigger. Started her on organic iodine. How long before lump goes down? Our fair is end of next week & it's an eye sore.

you can also add iodized salt to her feed or Kelp...
here is a good article on it..

http://www.tennesseemeatgoats.com/articles2/iodinedeficiency.html

Do I need to be careful about overdosing her?

According to Tenn. meat goats, a quick way to treat is to paint 7% iodine on her tail web. then I would offer free choice kelp will allow the goats to eat what they need and so over doseing is not a worry..also sprinkling iodized salt on her feed until the goiter goes away would be safe..

The article also says " Cobalt deficiency and its accompanying Vitamin B12 deficiency can also cause goiters." Adding B complex PLUS which is a good source of 12 could be given daily as well in case the goiter is from that...
she also mentions certain plants that can cause Iodine deficiency , so take a look at her list and see if you have any around

Ok went out and gave her a big shot of bcomplex plus.
Walgreens has 10% iodine tincture for much cheaper. Would that work?

10% might be a bit strong....Ive never used more than 7%

Good to have b complex plus on hand : ) Hopefully it helps and you see improvment..