Answer:
Snowballing
Step-by-step explanation:
Snowball sampling often referred to as chain-referral sampling is a method of sampling used in social statistic, which is defined as a non-probability sampling technique whereby the samples have characteristics that are rare to find. It is characterized by scenario in which the existing subjects provide referrals to recruit samples required for a research study.
Hence, in this case, Ingrid making use of Snowballing non probability sampling technique, since she is using those interested to be the subjects of the study to find more of the subjects to use as sample of the research.