viral traffic is possible if the video is free and public. Her videos are subscriber only. Scalabity is not a factor.
A simple video tag is good enough, you can store it on object storage (anyone but s3) . This she should do anyway for backup, any provider can kick her out for copyright violations and block her access to her own content.
Transcoding is not that difficult anymore video editing software allows you to transcode for the web directly . Unlike 5-10 years back every brower recognizes mp4 h264 today just one file is adequate.