Poppy seeds — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Contain trace opiates and can show up on a drug test. A few on bread are harmless.
Short answer
Her small size does mean the amount of seeds relative to her weight is higher, but a single bagel piece is still unlikely to cause poisoning. Poppy seeds contain trace opiates, but the few dozen seeds on a bagel are generally considered harmless for dogs. The main concerns would be a very rich, unfamiliar food upsetting her small stomach or, in extremely rare cases, a false positive on a drug test. Watch her for any vomiting or unusual drowsiness, and call your vet if she seems off.