Verbs ending in -ir that undergo stem changes in the present tense also under go stem changes in the preterite. These verbs have a stem change in the second person formal singular (usted), third person singular (él, ella) and third and second person plural (ellos, ellas and ustedes) forms.
It would be;
Antes mi hermanita le TENIA miedo a los perros.
TENIA is the past form.
Hope this helps (not sure if this is what you needed)
