1yr unspayed female cat pooping in werid places

(She's going to get fixed, it was postponed due to hookworms and some gastro issues. All of my cats are fixed and indoors only)

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The issue: when shes in heat she doesn't poop in the litter box, she deliberately goes in the bathtub / close to it if not in it.

Is this heat related??? Or just her being weird about where she shits when shes in heat??

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Thank you!!