That sound is the final sound of the word without the suffix.
If you know think "What final sound? SadIq ends in a consonant." this is not completely true. If there is a suffix or more words following there is a case ending. Duo tries to avoid diving into the case endings and they are usually omitted in dialects. However, if you want to know about the sound between SadIq and hA, we have to look into it.
For nominative (subject), you have a -un (indefinite) or -u (definite) suffix. For accusative (object), you have an -an or -a suffix, For genitive (possessor, after prepositions), you have an -in or -i suffix.
The possessive suffix defines the word. Therefore, we need the definite suffix. In this case, SadIq is the subject, so it is SadIq-u-hA.
If, for example, instead of her friend, it were her friend's friend, it would be SadIq-u SadIq-i-hA.
Dialects might be more forgiving about this sound in between.