If she hasn't been tested, I would absolutely do that. My youngest was diagnosed just before his second birthday. He was putting on a lot of weight, but not eating much more than our other boxer. Skin conditions are also an indicator of a thyroid imbalance.
The test may be more than you can comfortably afford (based on your comments), but the medication runs about $10/month if she ends up needing it.
Other symptoms of hypo-thyroid include:
Lethargic behavior such as a lack of interest in play, frequent napping, tiring out on long walks
Weight gain, sometimes without an apparent gain in appetite
Bacterial infections of the skin
Dry skin
Hair loss, especially on the trunk or tail (“rat’s tail”)
Discoloration or thickening of the skin where hair loss has occurred
Cold intolerance/seeking out warm places to lie down
Slow heart rate
Chronic ear infections
Severe behavioral changes such as unprovoked aggression, head tilt, seizures, anxiety and/or compulsivity
Depression
