How to raise the temperature of that girl Erica? (7)
I believe the answer is:
heather
'erica?' is the definition.
(plant genus including heather)
'how to raise the temperature of that girl' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'girl' could be 'her' and 'her' is present in the answer.
This explanation may well be incorrect...
(Other definitions for heather that I've seen before include "Girl" , "Small purple evergreen plant growing on hills" , "grows wild" , "Calluna vulgaris" , "Low shrub; mixed-colour (yarn)" .)